The present invention, in some embodiments thereof, relates to mechanical supports for bodily vessels, and in particular to external supports for elongated blood vessels such as peripheral or coronary arterial bypasses grafts.
Arterial occlusive disease, most commonly atherosclerosis, underlies most peripheral arterial disease. Most of the atherosclerotic blockages are found in the lower extremity. As vessel narrowing increases, critical limb ischemia (CLI) can develop when the blood flow does not meet the metabolic demands of tissue at rest. While CLI may be due to an acute condition such as an embolus or thrombosis, most cases are the progressive result of a chronic condition, most commonly atherosclerosis.
A peripheral vascular bypass, also called a lower extremity bypass, is the surgical rerouting of blood flow around an obstructed artery that supplies blood to the legs and feet. The three common peripheral vascular bypass surgeries are aortobifemoral bypass surgery, which reroutes blood from the abdominal aorta to the two femoral arteries in the groin; femoropopliteal bypass surgery, which reroutes blood from the femoral artery to the popliteal arteries above or below the knee and femorotibial bypass surgery, which reroutes blood between the femoral artery and the tibial artery. A substitute vessel or graft must be used in bypass surgeries to reroute the blood. The graft may be a healthy segment of the patient's own saphenous vein (autogenous graft), a vein that runs the entire length of the thigh. A synthetic graft may be used if the patient's saphenous vein is not healthy or long enough, or if the vessel to be bypassed is a larger artery that cannot be replaced by a smaller vein.
In recent years, angioplasty has supplanted peripheral bypass surgery as the first-line therapy for patients with CLI. Endovascular revascularization has become acceptable as a minimally invasive technique that is associated with low morbidity and mortality, reduced hospital costs, and decreased length of hospitalization. The main tradeoff is shorter durability when compared with the surgical alternative, which is still considered optimal strategy for patients that are capable of withstanding an open surgical procedure, and having life expectancy of over two years.
Intimal hyperplasia and tissue modulation are still considered main cause of vein graft failures in arterial bypass surgeries. These failures are accompanied by significant amounts of disability and limb loss resulting in increased resource utilization for the health care system and in a diminished quality of life for the patient. Veins placed in the arterial circulation as bypass conduits are universally subjected to acute increases in pressure and pulsatile hemodynamics, resulting in acute increases in wall shear and radial stress. Trauma during harvesting, pre-bypass morphological changes, and ischemia reperfusion during the procedure may impact the ability of the vein to adapt to these forces.
Externally supporting the graft with an external device has the potential to reduce wall stress and cyclic stretching of medial and endothelial cells and reduce diameter mismatch between the vein graft and the artery, all of which might be expected to reduce wall thickening. The efficacy of external support to the graft has been studied by several groups over the past few years and the findings from pre-clinical studies demonstrated significant inhibition of neointimal formation, reduction of atherosclerosis plaques and overall graft thickening reduction comparing to non-supported grafts.
Prior publications describing grafts provided with external supports or layers commonly suggest bonding of the external support to selectively cover the graft, optionally by using glue or sutures. Exemplary publications include U.S. Pat. No. 5,755,659 to Zurbrugg and U.S. Pat. No. 7,998,188 to Zilla et al., the disclosures of which are fully incorporated herein by reference. Such grafts may be provided to the medical practitioners readily covered and supported, or that the medical practitioners or their supporting team are instructed to bond the graft and the external support together prior to grafting. The latter scenario may be time consuming and bothersome to the medical team and may derive special training and expertise in materials bonding and preparations so that the finalized artifact will be satisfactory prepared in a timely manner.
International patent application published as WO 2010/058406 to Orion et al., the disclosure of which is fully incorporated herein by reference, describes a plastically deformable external support which further allows shaping and casting of the graft once deployed thereto. The plastic deformity allows the practicing surgeon to shape such external supports to a self-fixating form characterized with a final length, diameter and/or contour, with minimal elasticity and/or spring-back, thereby diminishing the need to use other means to maintain relative positioning and coverage of the graft and the external support.
Further needs stand out when a graft is substantially long, as for example in peripheral bypass surgeries, where it is common to use grafts which are longer than 20 cm and may even extend up to 50 cm, 60 cm and even more. External supports covering long vein grafts in legs and arms, for example, are prone to encounter substantial axial forces, shortening and/or fraying caused by internal radial pressure or by external forces commonly associated with proximity to skin surface and normal function of the limb. Therefore, there is a need to develop external supports also for supporting long grafts, being capable of resisting axially compressing forces while substantially maintaining chosen length, diameter and/or structure while not shifting or displacing from a needed vein graft coverage form, and while obviating the need for external bonding means such as adhesives, clips and sutures.